Anti-skid brake systems for automotive vehicles, particularly heavy trailer trucks, are well known in the prior art. Examples of some of these systems in the patented prior art are contained in the following U.S. Pat. Nos.: 2,868,388, 3,809,437, 3,503,654, 3,836,209, 3,779,613, 3,932,000, 3,782,785, 3,981,545, 3,782,786, 3,985,400.
As reflected in the above-noted prior art patents, the development of anti-skid brake systems particularly for trucks has become very sophisticated and the systems are complex and quite costly. Some prior art systems are primarily electrical in their operation while others are primarily mechanical with various fluid circuit components. In general, the prior art systems are too complex and costly for practical applications to automobiles and tend to be over-engineered for this important purpose.
In light of the above, the objective of the present invention is to provide a greatly simplified and much less costly and therefore more practical anti-skid brake control system, primarily adaptable to automobiles but also usable on trucks and other heavy vehicles. The invention, while being stripped of much of the complexity of the prior art, still retains the important and necessary operational and safety capabilities of the known pulsating type anti-skid systems. The invention involves the introduction of only a single unitized pumping or pulsating component in any conventional hydraulic brake system between the master cylinder and the wheel brake cylinders. This unit which embodies the invention can readily be installed on existing vehicles or can be incorporated as original equipment on new vehicles with only a small increase in cost while greatly enhancing the safety of the vehicle.
The pumping or pulsating unit contains a ported piston which, in one position under influence of spring pressure, has its port in registration with the fluid line extending between the master cylinder and the several wheel cylinders. In a retracted position against spring pressure under influence of a solenoid controlled by a pressure switch, the piston blocks or closes the fluid line between the master cylinder and wheel cylinders and creates a suction through a port in the pumping unit which is in communication with the main line leading to the wheel cylinders, thereby relieving pressure on the wheel cylinders and associated brake shoes. The retracted piston is released automatically by the solenoid and is returned by spring pressure to the position where the piston port again registers with the main fluid line leading to the wheel cylinders and this re-establishes pressure in the wheel cylinders to reapply the brakes. This operation is repetitive or cyclical while foot pressure is continuously applied to the brake pedal of the vehicle. The pulsating brake operation which can be adjusted is estimated at a practical rate of five pulsations per second, but in some cases could be much higher, as in the range of 100 or more pulsations per second.